This invention relates to water-insoluble violet benzimidazolone monoazo pigments and processes for their preparation.
A number of water-insoluble violet benzimidazolone monoazo pigments are known, for example as described in U.S. Pat. No. 3,118,870 (Dietz et al.), U.S. Pat. No. 3,137,686 (Dietz et al.), U.S. Pat. No. 3,609,135 (Ribka), U.S. Pat. No. 4,312,807 (Fuchs), U.S. Pat. No. 4,555,568 (Hunger), DE Patent No.1,188,229, DE Patent No.1,215,839, UK Patent No.1,238,896 and UK Patent No.2,015,015.
It is an object of the invention to provide water-insoluble violet benzimidazolone monoazo pigments which display high thermo resistance and good fastness to migration.
According to the invention, water-insoluble violet benzimidazolone monoazo pigments have two benzimidazolone rings in the pigment molecule and the following general formula: 
wherein R1, R2 and R3 each represent hydrogen, chlorine, bromine, methyl, methoxy, ethoxy, nitro or a group of the formula xe2x80x94COOR with R being hydrogen, methyl or ethyl, and R4 represents hydrogen, chlorine, bromine, methyl, methoxy, ethoxy or nitro group.
R1 may be methyl and R2, R3 and R4 may be hydrogen. Alternatively, R1, R2, R3 and R4 may each be hydrogen.
A monoazo pigment in accordance with the invention may be prepared by coupling the diazonium salt of an amine of the formula: 
wherein R1, R2, and R3 are as defined above, with a compound of the formula: 
wherein R4 is as defined above.
Diazonium salts of the following amines may be used for coupling:
5-amino-benzimidazolone-(2)
5-amino-6-methyl-benzimidazolone-(2)
5-amino-6-methoxy-benzimidazolone-(2)
5-amino-6-ethoxy-benzimidazolone-(2)
5-amino-4-chloro-benzimidazolone-(2)
5-amino-6-chloro-benzimidazolone-(2)
5-amino-7-chloro-benzimidazolone-(2)
5-amino-7-methyl-benzimidazolone-(2)
5-amino-7-methoxy-benzimidazolone-(2)
5-amino-7-ethoxy-benzimidazolone-(2)
5-amino-4,6-dichloro-benzimidazolone-(2)
5-amino-4,6,7-trichloro-benzimidazolone-(2)
5-amino-6-nitro-benzimidazolone-(2)
5-amino-benzimidazolone-6-carboxylic acid
5-amino-benzimidazolone-6-carboxylic acid methyl ester
5-amino-benzimidazolone-6-carboxylic acid ethyl ester
The coupling component used in the present invention for the preparation of the monoazo pigments can be prepared by known methods, for example by reacting 2-hydroxy-3-naphtoic acid chloride with 5-amino-benzimidazolone-(2).
There may be also be used the corresponding derivatives substituted in the benzene nucleus of the benzimidazolone radical, as for example:
5-(2xe2x80x2-hydroxy-3xe2x80x2-naphtoylamino)-6-chloro-benzimidazolone-(2)
5-(2xe2x80x2-hydroxy-3xe2x80x2-naphtoylamino)-7-chloro-benzimidazolone-(2)
5-(2xe2x80x2-hydroxy-3xe2x80x2-naphtoylamino)-6-methyl-benzimidazolone-(2)
5-(2xe2x80x2-hydroxy-3xe2x80x2-naphtoylamino)-7-methyl-benzimidazolone-(2)
5-(2xe2x80x2-hydroxy-3xe2x80x2-naphtoylamino)-7-ethoxy-benzimidazolone-(2)
5-(2xe2x80x2-hydroxy-3xe2x80x2-naphtoylamino)-7-bromo-benzimidazolone-(2)
5-(2xe2x80x2-hydroxy-3xe2x80x2-naphtoylamino)-6-methoxy-benzimidazolone-(2).
Diazotisation may be performed by known methods.
Coupling may be carried out by gradual addition of the acid solution of the diazonium salt to the aqueous suspension of reprecipitated coupling component in a slightly acidic medium, preferably at a pH of 4 to 6.
Coupling can be also carried out by simultaneous addition of the aqueous alkaline solution of the coupling component and the acetic solution of the diazo salt into a buffer. Suitable buffers are for example the alkali salts of formic acid, phosphoric acid or especially acetic acid.
Coupling is performed advantageously in the presence of agents promoting coupling. Those which may be mentioned are in particular nonionic, cationic or anionic dispersing agents, for example arylalkylsulfonates, such as dodecylbenzenesulfonate, alkylbenzenesulfonates, alkylnaphthalenesulfonates, fatty acids, for example palmitic acid, stearic acid and oleic acid, alkali metal salts of fatty acids, naphthenic acids and resin acids, cationic substances, such as quaternary ammonium salts, N-oxides of tertiary amines or their salts, fatty amines and their ethoxylated derivatives, and nonionic substances such as fatty alcohol polyglycol ethers and polycondensation products of ethylene or propylene oxides.
The surface-active agents can be added either alone or as a mixture. The amount can vary within wide limits, the quantity which is generally used being 0.1 to 20% by weight, preferably 2 to 10% by weight, relative to a 100% pigment yield.
The coupling component solution can also contain protective colloids, for example methyl cellulose, or small amounts of inert organic compounds, sparingly soluble or insoluble in water, for example aromatic hydrocarbons, such as toluene, xylene. chlorobenzene or nitrobenzene, as well as aliphatic halogenated hydrocarbons, for example carbon tetrachloride, also organic solvents miscible with water, such as acetone, methyl ethyl ketone, methanol, ethanol or isopropanol, or preferably dimethylformamide.
Some of the pigments obtained by this invention possess a hard grain. In order to obtain the full tinctorial strength they may be heated in the form of their reaction mixture under pressure to temperatures above 100xc2x0 C. using a closed pressure vessel. Alternatively, the crude pigment can be first isolated, washed free of salt and subsequently heat-treated in an aqueous or aqueous-solvent containing suspension at temperatures above 100xc2x0 C., preferably 120xc2x0 C. to 180xc2x0 C.
A further variant of the after treatment with solvents consists of stirring the moist filter cake with a suitable solvent, distilling off the water and heating the suspension free from water to a temperature above 100xc2x0 C., removing the solvent by distillation or filtration and isolating the pigment.
Suitable solvents to be added to the suspension are for example toluene, xylene, chlorobenzene, o-dichlorobenzene, nitrobenzene, pyridine, quinoline, methanol, ethanol, isopropanol, n-butanol, isobutanol, glycol monomethyl ether, glycol monoethyl ether, acetone, methylethyl ketone, dimethylformamide, dimethylsulfoxide, dimethylacetamide, N-methylpyrrolidone and tetramethylene sulfone.
Finally, coupling can also be carried out by suspending the amine and the coupling component in a molar ratio of 1:1 in an organic solvent and treating the suspension with a diazotising agent, especially an ester of nitric acid, such as methyl nitrite, ethyl nitrite, butyl nitrite or amyl nitrite.
The products according to the present invention are valuable pigments which can be used in all pigment application fields. They are particularly interesting for coloring high-molecular weight materials because of their excellent fastness to migration. Because they contain two 5-membered heterocyclic rings in the molecule, they display high thermoresistance. The pigments can be used in the coloration of plastics, coatings and inks.